Jose, there was an article in Traditional Bowhunter a year or two ago on doing this. You don't use household bleach I know for sure. I think they use the stuff hairdressers use for bleaching hair-peroxide
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I do not seek the good of others as a sanction for my right to exist, nor do I recognize the good of others as a justification for their seizure of my property or their destruction of my life.- Hank Rearden
Are you wanting the skull white... or the horns themselves? Tim's spot on with the TBM article on the skull... but it might work on the horns also... as if I remember right they said to keep them out of the mix...